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Will Deacon
88b0193d94
Perf can generate and record a user callchain in response to a synchronous request, such as a tracepoint firing. If this happens under set_fs(KERNEL_DS), then we can end up walking the user stack (and dereferencing/saving whatever we find there) without the protections usually afforded by checks such as access_ok. Rather than play whack-a-mole with each architecture's stack unwinding implementation, fix the root of the problem by ensuring that we force USER_DS when invoking perf_callchain_user from the perf core. Reported-by: Al Viro <[email protected]> Signed-off-by: Will Deacon <[email protected]> Acked-by: Peter Zijlstra <[email protected]> Cc: Alexander Shishkin <[email protected]> Cc: Arnaldo Carvalho de Melo <[email protected]> Cc: Jiri Olsa <[email protected]> Cc: Linus Torvalds <[email protected]> Cc: Thomas Gleixner <[email protected]> Signed-off-by: Ingo Molnar <[email protected]>